In a normal heart, four heart valves control the passage of blood between the chambers in the heart. These valves control unidirectional fluid flow of the blood. State of the art medical techniques have enabled specialists to replace defective heart valves with prosthetic heart valves.
An example of a state of the art prosthetic heart valve is disclosed in the U.S. Pat. No. 4,532,659 to Kaster, issued Aug. 6, 1985. The valve includes a free floating rotatable, pivotable disk occluder mounted for pivoting movement on a proximally positioned control unit. The control unit defines an off center fulcrum upon which the disk occluder pivots between an open and a closed position. In operation, when blood pressure on the proximal side of the disk occluder increases and exceeds the blood pressure on the distal side of the disk occluder, the disk occluder moves from an occluded or closed position to the open position. This transition between open and closed positions is actuated purely by the asymmetric blood pressures on the inlet and outset sides of the disk occluder. There is no additional means for controlling either the opening or closing of the valve.
The U.S. Pat. No. 3,974,854 to Kurpanek, issued Aug. 17, 1976 discloses a permanently implantable artificial heart including a unidirectional fluid flow valve. Each valve includes two valve flaps which open in response to an increased blood pressure gradient on the inlet side of the flaps and close due to magnetic attraction when the blood pressure gradient reverses. The valve flaps contain a permanent magnet which is magnetically attracted to a permanent magnet mounted rigidly in the outer wall of the support structure. This device includes means for actuating the closing of the valve flaps but includes no means for controlling the opening of the valve flaps independent of the blood pressure gradient on the two sides of the valve flaps.
The U.S. Pat. No. 4,605,408 to Carpentier, issued Aug. 12, 1986, discloses a cardiac valve having a device which insures controlled opening of the valve when blood pressure is balanced on both sides of the mobile element or disk occluder of the valve. The mobile element of the valve is either mechanically moved to an open position by a spring when the pressure on the mobile element is equal on both sides or the valve includes magnets disposed opposite each other, the poles of the same sign facing each other. One of the magnets is within the ring about the mobile element and the other magnet is embedded within the mobile element. The two magnets repulse each other thereby opening the valve slightly when the pressures on each side of the valve are equal.
It is desirable, experimentally and clinically, to be able to control when a prosthetic heart valve opens. Experimentally, it is beneficial for researchers to be able to manipulate the flow of blood through the heart under controlled experimental conditions. Clinically, the control of the opening of the valves, as well as the control of the closing of the valves, provides the clinician with new tools for therapeutic application.